It is known that certain chemical compounds permit the formation of glass, either singly or in combination with other compounds or components. Glasses in which the formative agent is a halide are relatively rare although the vitrifying properties of beryllium fluoride have been known for a long time. Glasses obtained with this compound are, however, costly and toxic. Moreover, the glass formative properties of aluminum fluoride have also been known for a long time.
Recently, glasses based on ZrF.sub.4 and HfF.sub.4 as well as glasses based on the fluorides of trivalent transition elements such as gallium, iron, chromium, vanadium, iridium or rare earth metals have been described principally in published French patents Nos. 76.18878, 77.09618, 79.07785, 80.06088 and 80.18139.
The capability of a material to form glass, either alone or in combination with other materials, is generally manifested by the fact that the material or a mixture of components, when melted, produce the glass if it is cooled at an accessible known rate. Although present technology permits the use of hypertempering, most of the glass in accordance with the present invention can be produced by casting liquid glass in a narrow mold or by flattening the molten mixture between two metallic elements. Binary glasses require, in general, a very rapid temper. All these glasses of the present invention can also be obtained in vitreous form by evaporation under vacuum and condensation on a substrate, the temperature of which can be modulated depending on the nature of the glass. This latter technique is equivalent to an extremely high liquid cooling rate.
The halogenated glasses of the present invention yield vitrifiable ternary and even binary combinations.
It results from the very nature of the glass that the addition of a third element to a binary system generally does not prevent the formation of glass, but more often favors it by virtue of the classic principle of "confusion" which states that an increase in the number of components leads to a lowering of a tendency to recrystallization. From this fact, the existence of binary glasses implies the existence of numerous ternary glasses by the addition to the former of a component. In the same manner, a ternary glass generates automatically several families of quaternary glasses by the addition of a fourth chemical compound thereto.
The halogenated glasses of the present invention can be prepared at relatively low temperatures.
Their principal interest and use resides in their wide applicability in the field of optical transmission, including the infra-red zone. Except in the particular case of glasses containing colored elements, the glasses of the present invention are transparent ranging from the ultra violet to the infra-red beyond 10 microns and they exhibit several technological advantages over previously known glasses, principally a larger optical opening and a value more lower than the theoretical minimum of losses by absorption, without exhibiting certain disadvantages observed for several families of halogenated glasses.
These properties impart to these glasses interesting characteristics and permit their use principally in the field of infra-red optics.
A particularly interesting use is that involving the production of optic fibers having a length sufficient to transmit infra-red. The uses of glasses transmitting infra-red, principally in the production of devices for the detection and study of thermal objects are well known to experts.